where
\(A_{\rm s} \)  is the amplitude, \(n_{\rm s}-1 \)  is the tilt and \(k_*\)  is a
fiducial momentum, chosen at one's convenience.
The flat spectrum in this parametrization has \(n_{\rm s}=1\) .
This is inconsistent with the
cosmological data, which give [1]}
\(n_{\rm s} = 0.968 \pm 0.06 \; .\) 
